1. Field of the Invention
The present invention relates to a structure for connecting a metal pipe and, more particularly, to an improvement in a flared double-wall structure which is formed at one open end of a metal pipe to be connected to one end of a mating joint. The metal pipe has a relatively small diameter and thickness, e.g., a diameter of 20 mm and a thickness of 1.5 mm or less and is generally arranged for oil or air feed passages in an automobile or a variety of machines or apparatus.
2. Description of the Prior Art
A flared double-wall structure of this kind for the connection according to the prior art is shown in FIG. 4. In this structure, one open end 11' of a pipe P' to be connected is so flared at 11 that it is formed of a conical wall 12 opened outward merely smoothly. For the connection, the flared double-wall structure is fastened and firmly clamped between the pressure receiving seat of a mating joint 13 and the pressure seat of a nut 14.
In this prior art, however, the double-wall flare 11 has its seat made to abut in a facial contact all over its face against the pressure receiving seat of the partner by the flatness of the conical wall 12, so that its facial pressure is reluctant to rise and feasible to cause a leakage. Moreover, an excessive fastening is invited to prevent the leakage at the mating pressure receiving seat due to a dispersion in the bent shape of the pipe P'. On the other hand, concentrations of fatigue and stress are caused at the neck of the double-wall flare 11 due to the structural limitation such as the small thickness of the pipe P' itself and the state of arrangement under vibrations. Thus, the structure of the prior art is frequently troubled by a cracking or breakage.